Heretofore, in such as the serger, the double chain stitch sewing machine, or the interlock stitch sewing machine, the gas carrying threading device which is connected by a hollow looper thread guide which leads from a thread introduction portion which inserts the looper thread to a looper thread guide outlet of a loop-taker point of the looper and which feeds a looper thread by utilizing a flow of a pressurized gas which is supplied to the hollow looper thread guide is known. Herewith, a complicated thread guard is unnecessary and a threading that a handleability is easy can be performed. Therefore, there are no mistake of the threading, no protrusion of the thread in mid-process, and no entanglement of the inserted looper thread with other thread, and thereby the threading can be performed at once by the extremely easy operation (Patent document No. 1-No. 3).